Celiac disease (CD) is a chronic autoimmune disease that is HLA-DQ2/DQ8 haplotype restricted. Gluten, the major protein fraction of wheat, and related proteins in rye and barley are the triggering agents of the disease. Ingested gluten or its' derivative fractions (gliadin and subunits) elicit a harmful T cell-mediated immune response after crossing the small bowel epithelial barrier, undergoing deamidation by tissue transglutaminase (tTG) and engaging class II MHC molecules. While the earliest events leading to CD involves innate immune responses, evidence in the literature seems to suggest that a dysfunctional cross talk between innate and adaptive immunity is also an important pathogenic element in the autoimmune process of the disease. Under physiological circumstances, the intestinal epithelium, with its intact intercellular tight junctions (tj), serves as a key barrier to the passage of macromolecules such as gluten. When the integrity of the tj system is compromised, as in CD, a paracellular leak (“leaky gut”) and an inappropriate immune response to environmental antigens (i.e., gluten) may develop. While our knowledge about tj ultrastructure and intracellular signaling events have significantly progressed during the past decade, relatively little is known about their physiological regulation secondary to extracellular stimuli and their roles in diseases such as CD.
Zonulin is an endogenous paracrine signaling protein that appears to regulate epithelial and endothelial cell tight junction function in animals and humans (Fasano, A. Ann N Y Acad Sci. 915:pp214-22 (2000); Fasano, A. Gut. 49:pp159-62 (2001); Fasano, A. et al. Lancet 355:pp1518-19 (2000); and Wang, W. et al. J Cell Sci. 113:pp4435-40 (2000)), and whose prokaryotic analogues (eg., zonula occludens toxin, or “ZOT”) possess immune stimulating effects when applied to mucosal surfaces in mammals (Marinaro, M. et al. Infect Immun 67:pp1287-91 (1999); and Marinaro, M. et al. Infect Immun 71:pp1897-902 (2003). In celiac intestinal tissues and in in vitro, ex vivo, and in vivo animal experiments, gluten/gliadin cause rapid zonulin release and zonulin-dependent increases in permeability (Drago, S. et al. Scan J Gastroenterol. 41:pp408-19 (2006); Fasano, A. et al. Gastroenterol. 112:pp839-46 (1997); Ventura, A. et al. Gastroenterol. 117:pp297-303 (1999); Schuppan, D. Gastroenterol. 119:pp234-42 (2000); Norris, J. M. et al. JAMA. 293:pp2343-51 (2005); Clemente, M. G. et al. Gut. 52:pp218-23 (2003); and National Institutes of Health. Consensus Development conference Final Statement dated Aug. 9, 2004. NIH consensus Development Conference on Celiac Disease. Bethesda, Md. Jun. 28-30, 2004) in normal and diseased states. Animal models likewise have demonstrated the association of gluten, increased paracellular permeability and other autoimmune diseases, including type 1 diabetes (T1D).
AT-1001 (Larazotide Acetate) is an orally administered octapeptide (Gly Gly Val Leu Val Gln Pro Gly (SEQ ID NO:15), that appears to inhibit gliadin-induced tj disassembly by blocking putative zonulin receptors on the luminal surface of the small intestine. Pretreatment with the peptide fails to inhibit gliadin induced zonulin release, while administration of zonulin analogues or gliadin in the presence of AT-1001 fail to significantly increase intestinal permeability, confirming that the effect of the molecule is specific to the zonulin receptor (Wang, W. et al. J Cell Sci. 113:pp 4435-40 (2000); and Drago, S. et al. Scan J. Gastroenterol. 41:pp 408-19 (2006)). Experiments with ex vivo human tissue and in mice demonstrate that AT-1001 blocks zonulin binding to its putative receptor, blocks the peak of F-actin increment induced by gliadin and inhibits gliadin induced reduction in intestinal Rt (resistance) (Wang, W. et al. J Cell Sci. 113:pp 4435-40 (2000); Drago, S. et al. Scan J. Gastroenterol. 41:pp 408-19 (2006); and Clemente, M. G. et al. Gut. 52:pp 218-23 (2003)). Furthermore, intranasal pre-administration of AT-1001 in mice prevented the ZOT-induced immune response to non-self antigen challenge (Marinaro, M. et al. Infect Immun. 71:pp 1897-902 (2003)).